OBJECTIVE To measure a profile of hormones in a group of elite athletes. Increasing awareness of the widespread use of hormones as performance-enhancing agents focusses attention on what may be considered as normal in this unusual group. DESIGN Blood samples were obtained from 813 volunteer elite athletes from a cross-section of 15 sporting categories. An endocrine profile was measured on a subset of 693. PARTICIPANTS Volunteer elite athletes. Samples were drawn within two hours of an event at a major national or international competition. MEASUREMENTS Demographics and hormone profiles were obtained on 454 male and 239 female elite athletes. RESULTS Hormone profiles showed significant differences in 19 of the 24 measured variables between sexes and between all of the 15 sporting disciplines in men and 11 out of 24 in women. 16.5% of men had low testosterone levels, whereas 13.7% of women had high levels with complete overlap between the sexes. Women had a lean body mass 85% that of men - sufficient to account for sex differences in performance. There were highly significant correlations between many of the measured hormones. CONCLUSIONS Hormone profiles from elite athletes differ from usual reference ranges. Individual results are dependent on a number of factors including age, gender and physique. Differences in profiles between sports suggest that an individual's profile may contribute to his/her proficiency in a particular sport. The IOC definition of a woman as one who has a 'normal' testosterone level is untenable.